(1) Field of the Invention
The present invention relates to a status change monitoring apparatus, and more particularly, relates to a status change monitoring apparatus by the use of direct memory access control (DMA) for collecting alarm data or status data of an apparatus to be monitored (herein after referred to as a monitored apparatus) such as radio equipment installed in the land stations in, for example, a satellite communication system.
(2) Description of the Related Art
A cross reference related to the present invention is Japanese Patent Publication (Kokai) No. 61-267825 laid open to public on Nov. 27, 1986. This reference discloses a character series searching system which enables a detection of a character series from data stored in an external memory during data transfer by means of DMA.
In general, a monitoring apparatus sends a data request signal to each monitored apparatus, and in response to the data request signal, the monitored apparatus returns data obtained by the monitoring. This communication is known as a polling system.
In a conventional status change monitoring apparatus, all bits of the received data are checked by a software process in a central processing unit to determine whether there is a status change in each bit of the received data. If there is a change, a corresponding lamp is lighted or an indication of the change of status is displayed on a CRT display.
There are, however, problems in the conventional status change monitoring apparatus. First, since the CPU checks all bits of data regardless of whether or not there is a status change, it requires too much software processing time especially when the data length is long or when there are too many monitored apparatus. Second, since the CPU takes care of the display operation for all bits of received data, it also requires too much software processing time so that the response time to display, to light a lamp, to drive a buzzer, and so forth is too long.